JPH0442724A - Overcurrent protective unit for power converter - Google Patents

Abstract

PURPOSE:To realize overcurrent protection and abnormal voltage protection corresponding to the characteristics of a battery power supply, without causing increase of the size and the cost, by outputting a control signal for blocking overcurrent when a current signal exceeds the level of a set signal. CONSTITUTION:A current signal generating circuit 30 outputs a current signal C in which a set signal b from a setter 31 is added, as a bias voltage, to a detection signal (a) of current If. A set signal (h) is reverse proportional to a voltage Vf and overall level can be regulated based on a bias voltage (f). The current signal C and the set signal (h) are fed to the comparator 41 at a control section 40 and when the current signal C exceeds the level of the set signal (h), a trigger signal (i) is fed to a flipflop 42 thus producing a control signal (i) for commanding overcurrent protection. The control signal (i) turns an inverter driving signal OFF and provides a trip signal to a trip coil 53 thus interrupting a circuit breaker 2.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is useful for switching purposes in power converters such as fuel cells and solar cells, which have a T-cell as a power source, which has a large output voltage drop with respect to an increase in output current. The present invention relates to an overcurrent protection device that protects semiconductor devices from overcurrent or surge voltage caused by overcurrent.

[Conventional technology]

Conventionally, the overcurrent protection Fj of power converters has been implemented by setting the overcurrent protection level to a constant value in the range of 120% to 150% of the rated current, for example by installing an overcurrent relay, etc. It is known to ensure that when a current occurs, the switching element stops flowing or the circuit breaker trips.

[Problem to be solved by the invention]

Figure 4 is a typical current and voltage waveform diagram of a switching semiconductor device used in a power converter. When the current generator f is controlled on and off, the surge voltage V changes to the steady voltage Vf K when the current generator f is switched off. It is known that the switching semiconductor element will be damaged if the abnormal voltage generated in a superimposed manner and consisting of the sum of both voltages Vf1V exceeds the limit level of the element withstand voltage shown by the broken line in the figure. Furthermore, it is known that the magnitude of the surge voltage V at this time is expressed by v=L −dif /dt, where L is the inductance of the circuit.

Figure 5 shows the output voltage-current characteristics (Vf-■f%) of the fuel cell.
This is a characteristic diagram showing the short-circuit current Ifs in comparison with the short-circuit current Ifs, and shows a downward-sloping characteristic where the output voltage VfFi of the fuel cell is highest in the no-load state and decreases steeply as the output current f increases. It is well known that the short-circuit current Ifs that flows when a load circuit is short-circuited is also represented by a downward-sloping curve that is almost similar to the Vf-F characteristic, and that a large short-circuit current flows in no-load or light-load conditions. On the other hand, the applicant of the present invention has revealed that in a state b where the output current f is large and the short-circuit current fs becomes small, such as during a rated load.

On the other hand, the switching semiconductor element power; the surge voltage V generated when switching off increases in proportion to the time change of the element current f. Considering the short circuit current fs of the fuel cell as a power source, If a short circuit occurs under light load or under constant load, it is expected that the stain pressure jump Jc 夛V will be large, and the output voltage Vf of the fuel cell will also be high when the load is light. , it is estimated that there is a high risk that the abnormal voltage vt''+v, which is the sum of both voltages, will exceed the withstand voltage limit of the switching element.

Considering the conventional method of overcurrent protection based on the above study results, if the overcurrent protection level was kept at a constant value larger than the rated current, the protection level would be too high at light loads, and short circuits could occur. It is expected that the risk of damage to the switching elements due to the abnormal voltage that occurs cannot be sufficiently avoided.

In addition, in order to avoid this situation, it is possible to use a switching semiconductor element with increased snubber capacity and a high p,it voltage threshold, but these measures are difficult to implement due to the large size of the power converter. The drawback is that it leads to increased costs and increased costs.

An object of the present invention is to obtain a current carrying protection device that can perform overcurrent protection and abnormal voltage protection corresponding to the characteristics of a battery power source without increasing the size of the device or increasing costs.

[Means to solve the problem]

In order to solve all of the above problems, the present invention provides a power converter that is connected to the output side of a battery power source with a large voltage drop with respect to the output current via a circuit breaker to control the output power.
The protection is based on the protection level determined by the short-circuit current characteristics of the battery power source, and includes a current detector and a voltage detector arranged on the input side of the power converter, and an adjustment to the detected voltage of the voltage detector. a setting signal generation circuit filter a that applies a bias voltage of possible opposite polarity, moves in parallel in reverse l-polarity, and then inverts and outputs it as a setting signal for the overcurrent protection level; A current signal generation circuit that outputs a current signal by applying an adjustable bias voltage of the same polarity, and a control signal that compares this current signal with the setting signal and prevents overcurrent when the current signal exceeds the level of the setting signal. and a control circuit that outputs an output to the control section of the power converter or circuit breaker.

[Effect]

In the configuration of the present invention, the overcurrent protection level setting signal output by the design signal generation circuit is approximately inversely proportional to the voltage-current characteristic of the battery power source, and this is inversely proportional to the short-circuit current versus load current characteristic of the battery power source. It is also inversely proportional to Therefore, the control circuit detects that the output signal of the ti-fold signal generation circuit exceeds the set signal level, and controls the flow of the power converter using the output control signal.
In light load areas where the output voltage and short circuit are large, overcurrent is detected early at a low level to provide abnormal voltage protection, and when the steady current is large and the rated load is high, overcurrent is detected at a high level. It is possible to perform overcurrent control corresponding to the magnitude of short-circuit current and steady-state current, and to prevent damage to switching elements by early suppressing abnormal voltage at the time of switching off, which increases when the load is light.

〔Example〕

The present invention will be explained below based on examples.

Fig. 1 is a connection diagram showing the configuration of an overcurrent protection device for a power converter according to an embodiment of the present invention, and Fig. 2 is a time diagram showing the signals of each part of the device shown in Fig. 1 in response to time changes in current. In Figure 0, the structure and operation of the device will be explained based on both figures below. In Figure 0, a fuel cell 1 is a pair of fuel gas and oxidant gas supplied from a reactant gas supply system (not shown) with an electrolyte sandwiched between them. The generated power is supplied to an inverter 6 as a power converter via a circuit breaker 2, and an inverter control circuit 7 is connected to an AND gate 9. Based on the command signal sent to the base drive circuit 8 through the entire inverter 3, current flow control of the switching semiconductor elements of the inverter 3 is performed. Further, the output of the inverter 3 is waveform-shaped by a filter 4, voltage-adjusted by a transformer 5, and then supplied to a load 6.

On the other hand, on the output side of the fuel cell 1, a detector 11 for the input current f of the inverter 3 and a detector 12 for the input voltage Vf are provided. The overcurrent protection device includes a current signal generation circuit 60 that receives the detected current f (signal a) of the current detector 11 as an input signal, and a detected voltage Vf (signal d) t of the voltage detector 12.
- It is composed of a generation circuit 20 which generates an overcurrent protection level setting signal as a human input signal, and a control section 40 which generates a control signal j that instructs to keep the current flowing S when the current signal exceeds the protection level.

Assume now that the detection signal a of the current f detected by the current detector 11 increases linearly with time as shown in FIG. A current signal generation circuit 30 comprising a P amplifier 32 outputs a signal added to the detection signal a as a current signal C as a setting signal b=2 bias voltage of the setting device 31. On the other hand, the detection signal d of the voltage Vf detected by the voltage detector becomes a curve that decreases in inverse proportion to the increase in the current factor f, as shown in FIG. This detection signal d is amplified by the first-stage OP amplifier 21 of the setting signal generation circuit 20, and is added as a bias voltage with the negative polarity setting voltage of the setting device 22 in the next-stage OP amplifier 26. signal d
The signal g is obtained by moving parallel to the negative side, and the third stage O
It is output as a setting signal with the polarity reversed by the F amplifier. In other words, the setting signal is inversely proportional to the voltage Vf, and the overall level can be adjusted (translated) by the bias voltage f. Furthermore, as already explained based on FIG. 5, the setting signal is inversely proportional to the voltage Vf. However, the signal has an inverse proportional relationship.

The current signal C and the setting signal R, which are the output signals of both generation circuits, are input to the comparator 41 of the control unit 40, and as shown in FIG. 2, when the current signal C exceeds the level of the setting signal R, a trigger signal 1 is generated. is output. For example, assume that a short-circuit accident occurs in the load circuit at time tx, and the current factor f rapidly increases to the short-circuit current factor fs shown by the broken line in FIG.

At this time, the current signal C also rapidly increases to CB and the comparator 4
1 satisfies the condition that the signal CB is set, and the trigger signal 1 is input to the 7 lip-flop 42, so the 7 lip-flop 42Fi, which was in the reset state by the reset switch 43, is set by the trigger signal 1,
A control signal j2>E that instructs current protection is obtained. Therefore, the control signal j is supplied to the AND gate to turn on the inverter drive signal and stop the inverter output, and at the same time, a trip signal is sent to the trip coil 53 via the relay 51 to shut off the circuit breaker 2. An action is taken.

As mentioned above, the feature of the embodiment is that the setting signal generation circuit 20
The signal generated at the output voltage V of the fuel cell and supplied as the setting signal for the comparator 41Km current protection level
The circuit is configured to vary in inverse proportion to f or the short-circuit current f8, and the level of the setting signal and current signal C can be adjusted by the bias voltage f or f. That is, in a light load region where the steady voltage Vf and the short circuit current fs are both large and the abnormal voltage Vf 10V generated is also large, the level of the setting signal is low.
A protective action is performed by detecting the short-circuit current fs at a small level at an early stage, and a protective action is performed by detecting the short-circuit current fa when it exceeds the rated current R,t- due to the high level of the setting signal in the rated load area. This makes it possible to perform overcurrent protection and abnormal voltage protection for switching elements suitable for battery characteristics such as fuel cells that tend to generate high abnormal voltages in light load regions.

Figure 3 F! It is a characteristic diagram showing the protection level in the example. When the short-circuit current fs rises at a slope as shown in the figure with respect to time t, the protection device detects the short-circuit current fBt - small level fsl at light load. In the rated load area, the protective operation is performed by detecting a large short-circuit current fa, and in the light load area, the protective operation is performed at the point in time when the short-circuit current is small. The abnormal voltage is also low, thus making it possible to prevent failure of the switching elements due to abnormal voltage. Further, the operating point can be adjusted by the bias voltage, and an operating point suitable for the characteristics of the battery power source and the element configuration of the power converter can be easily selected.

〔Effect of the invention〕

As described above, the present invention is configured to compare a current signal with a setting signal that is inversely proportional to the detected voltage, and perform an overcurrent protection operation when the latter exceeds the former.

As a result, in response to the characteristics of battery power sources such as fuel cells and solar cells, which have a high voltage in the light load range and a high short-circuit current and resulting jump-up voltage at switching off, the short-circuit current It is possible to avoid damage to the switching elements caused by the high surge voltage that is likely to occur in the light load region, which has become a problem when the abnormal current is at a low level in the light load region. There is no need to take measures such as increasing capacity or using switching elements with high withstand voltage, and therefore overcurrent protection and overvoltage that match the characteristics of battery power sources can be achieved without increasing the size or cost of the power converter. A power converter equipped with a highly reliable overcurrent protection device that can provide protection can be provided. Furthermore, since the protection level can be easily adjusted using the bias voltage setting device, an advantage is obtained in that the optimum protection level can be freely selected in accordance with the characteristics of the battery power source, the element configuration of the power converter, and the like.

[Brief explanation of drawings]

Figure t41 is a connection diagram showing the configuration of a current protection device for a power converter according to an embodiment of the present invention, Figure 2 is a time chart showing changes in signals at each part in the embodiment, and Figure 3 is an overcurrent diagram in the embodiment. A characteristic diagram showing the operating point of protection, Figure 4 shows the typical current in the switching element of a power converter,
FIG. 5 is a voltage waveform diagram and a V-1 characteristic diagram in a fuel cell as a fuel cell power source. 1... Fuel cell (battery power supply), 2... Circuit breaker, 3...
...Inverter (power converter), 11...Current detector, 12...Voltage detector, 20...Protection level setting signal generation circuit, 21, 23, 24, 32...○P on-pull , 22.31... Bias voltage setting device, 60...
-Current signal generation circuit, 40...control unit, 41...
Conno (later, 42...7 lipflop, 51...
...Relay 56...Trip coil, If 9. Output current of the fuel cell, Vf... Output voltage of the fuel cell, f
s...Short circuit current, ■...Spring voltage (surge voltage), a...Current detection signal, C...Current signal, h...
・Protection level setting signal, representative patent attorney Otori Yamaguchi ・7: Motoko 9 Figure 4 gAg

Claims (1)

[Claims] 1) A power converter that is connected via a circuit breaker to the output side of a battery power source that has a large voltage drop with respect to the output current and controls the output power, is protected based on a protection level determined by the short-circuit current characteristics of the battery power source. and a current detector and a voltage detector arranged on the input side of the power converter, and after applying an adjustable bias voltage of opposite polarity to the detected voltage of the voltage detector and moving it in parallel to the opposite polarity. a setting signal generation circuit that inverts and outputs it as an overcurrent protection level setting signal; a current signal generation circuit that adds an adjustable bias voltage of the same polarity to the detected current of the current detector and outputs the detected current; a control circuit that compares the signal with the setting signal and outputs a control signal to the control section of the power converter or circuit breaker to prevent overcurrent when the current signal exceeds the level of the setting signal. An overcurrent protection device for a power converter, characterized in that: